1. Field of the Invention
This invention relates generally to multilayer, multichip module substrates. More particularly, the invention relates to a multilayer, multichip module substrate designed for enhanced heat dissipation.
2. Description of the Related Art
Heat transfer is an important consideration in electronics design and hence the design of multichip module substrates. The use of high density, high clock rate circuits, especially microcircuits and high-interconnect-density printed wiring assemblies, has been discouraged by the lack of effective heat removal.
A number of techniques have been devised to transfer heat from electronics. In U.S. Pat. No. 5,111,278, a multichip module system is described that includes thermal vias or channels to facilitate heat removal. The device disclosed in U.S. Pat. No. 4,764,804 uses a number of "bump" electrodes that are placed between chips to serve as heat transfer elements.
Since the thermal conductivity of typical chip dielectrics is poor, the thermal vias or bumps are placed directly under the chips populating the multichip module substrate. The vias or bumps provide a thermal path from the chips to the substrate, however they severely limit the routing density of the metalization underlying the chips.
In multichip module substrates made by the multichip module D (MCM-D) process, polyimides and silicon dioxide have been used as dielectric layer materials. Polyimides have a thermal conductivity on the order of 0.2 W/(m-K). Silicon dioxide has a thermal conductivity of 1.4 W/(m-K). These thermal conductivities impose severe design constraints on a multichip system.
A need exists for a multichip module substrate that dissipates more heat for the same area/volume allowing denser, higher speed, higher power electronic systems to operate within acceptable temperature ranges or allowing less dense, lower power, lower speed electronic systems to operate at lower operating temperatures.